Process for the production of ammonia

Abstract

A process for the production of ammonia comprises passing hydrogen and nitrogen over a catalyst comprising a transition metal, e.g. ruthenium, and a modifying metal, e.g. an alkali metal, supported on a graphite-containing carbon support having specified surface area properties. At start-up the nitrogen is supplied in stoichiometric excess and thereafter in stoichiometric proportions.

I claim: 
     
       1. A continuous process for the production of ammonia which process includes a start-up stage and a subsequent stage, said process comprising passing a feedstock containing hydrogen and nitrogen over a catalyst during both said start-up stage and said subsequent stage, the nitrogen and hydrogen being supplied at said start-up stage so that nitrogen is in stoichiometric excess and thereafter supplying make up feedstock of nitrogen and hydrogen in stoichiometric proportions, said catalyst comprising (i) as support a graphite-containing carbon having (a) a basal plane surface area of at least 100 m 2  /g, (b) a ratio of BET surface area to basal plane surface area of not more than 8:1, and (c) a ratio of basal plane surface area to edge surface area of at least 2:1, and (ii) as active component (a) 0.1 to 50% by weight of a transition metal of the 4th, 5th and 6th horizontal periods of Groups VB, VIB, VIIB and VIII of the Periodic Table, expressed as % by weight of total catalyst, and (b) 0.1 to 4 times by weight of (a) of a modifying metal ion selected from Groups IA or IIA of the Periodic Table or the lanthanides or actinides, the modifying metal ion being actively associated with the transition metal rather than the support, under conditions of temperature, pressure and space velocity such that conversion to ammonia is effected, separating unreacted hydrogen and nitrogen from product ammonia, recycling the unreacted hydrogen and nitrogen to said subsequent stage with the nitrogen in stoichiometric excess, and supplying make-up feedstock of hydrogen and nitrogen to said subsequent stage in stoichiometric proportions. 
     
     
       2. A process according to claim 1 wherein the graphite-containing carbon has a ratio of BET surface area to basal plane surface area of not more than 5:1 and a ratio of basal plane surface area to edge surface area of at least 5:1. 
     
     
       3. A process according to claims 1 or 2 wherein the transition metal is present in an amount of 1 to 30% by weight, expressed as % by weight of total catalyst. 
     
     
       4. A process according to claims 1 or 2 wherein the transition metal is ruthenium. 
     
     
       5. A process according to claims 1 or 2 wherein the modifying metal ions are rubidium or potassium ions. 
     
     
       6. A process according to claims 1 or 2 wherein the feedstock is passed over the catalyst at a temperature in the range 250° to 600° C., a pressure in the range atmospheric to 300 bars and a space velocity in the range 1,000 to 100,000 v/v/hr. 
     
     
       7. A process according to claim 6 wherein the feedstock is passed over the catalyst at a temperature in the range 300° to 500° C., a pressure in the range 20 to 200 bars and a space velocity in the range 5,000 to 30,000 v/v/hr. 
     
     
       8. A process according to claims 1 or 2 wherein the molar ratio of hydrogen to nitrogen at the entrance to the reactor is in the range 2:1 to 0.67:1. 
     
     
       9. A process according to claim 8 wherein the molar ratio of hydrogen to nitrogen at the entrance to the reactor is 1:1. 
     
     
       10. A process according to claims 1 or 2 wherein a purge stream is withdrawn from the recycle stream and a compensating make-up stream is supplied to the reactor to re-establish the desired ratio of hydrogen to nitrogen. 
     
     
       11. A process according to claims 1 or 2 wherein hydrogen is injected at an intermediate point or points along the reactor.